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The 200-island nation of the Maldives exists mostly within a meter of sea level. As seas rise, it's threatened, but changing temperature and ocean acidification are problems for seafood-eating residents, too. nicadlr/Flickr

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More than a billion people, many of then the poorest in the world, rely on fish and shellfish to survive. Their food supply is threatened by changes in the ocean wrought by carbon emissions: a second line problem of global warming.

The dual climate threats to ocean-based food security are temperature and chemistry. Temperature changes where fish live: in a warming ocean, generally, fish head away from the tropics and shallow waters, looking for the right temperatures in which they can feed and breed. It can also drive fish toward unexpected predators and make them invasive species, destabilizing ecological balance in different regions.

A more acidic ocean presents a related threat. Carbon has always cycled through the atmosphere; part of that flow is an exchange of carbon molecules between the atmosphere and the top layers of the world’s oceans. As humans have contributed more greenhouse gases to the atmosphere, more carbon makes its way into the ocean.

That’s changing the ocean’s pH level. Sea water’s higher acidity softens and decimates coral, a feeding zone for some marine life. It also weakens the shells of mollusks.

Oceana marine scientists looked at peer reviewed literature and publicly-available statistics to rank nations for climate related risks, ocean acidification related risks, and both combined. They looked at how dependent different nations are on ocean-related food for protein and sustenance, and how well nations can adapt to economic, political and social threat.

The study’s author admits some uncertainties remain. “We definitely don’t know exactly how organisms are going to react,” says Oceana marine scientist Matthew Huelsenbeck. “We have specific examples from the lab. But scaling it up to the entire ocean and how ecosystems will react to the removal of one species or many is a huge question mark.”

The nations most vulnerable to climate impacts on seafood are, in many cases island nations.

A 2011 documentary film, The Island President, chronicles the efforts by the government of the Maldives to call attention to sea level rise and other threats of a warming climate.

“The reason why Maldives is unique is because we’re going to lose an entire nation, an identity, a culture, all this,” said Aminath Shauna, then-climate coordinator for the Maldives. “There’s so many other countries but none of these countries are going to lose their entire national identity. We will.”

Oceana’s Huelsenbeck said a surprising finding in his research is that Persian Gulf nations like Iraq and Pakistan, as well as north African nations, like Libya and Eritrea, bear high risk from both phenomena.

“So I was surprised to find that there’s a lot of people there in those countries who still use old wooden canoes to fish for their resources,” says Huelsenbeck. “And they provide a lot of food to coastal communities in those countries. Often times we just think of them as big oil countries. But there are many people there living a subsistence life off of fish.”

Oceana and representatives of these countries aim to call attention to the ways human activity has widened the existing pipeline of carbon into the atmosphere and thereby into the seas.

In tropical island regions, that means more advocacy for shutting down that pipe. “Maldives is a frontline state,” President Mohammed Nasheed told climate negotiators in London, in the documentary in The Island President. “If you thought defending Poland and defending Vietnam was important, defending the Maldives is very important. And when you have millions and millions of people in similar predicaments, just imagine the impact it would have on world order.”

The US isn’t overly dependent on one risky source of seafood. What’s more, it has the economic power to protect itself better than these countries. But sea level rise, changing temperatures and ocean acidification are happening in waters off Alaska, California, the Gulf of Mexico, and northeastern states along the Atlantic too.

Military and political leaders recognize that destabilizing a country’s food supply can raise its risk for political instability internally and in the region it occupies. Oceana’s Huelsenbeck says the goal of his report is to redefine the scope of field for ocean-related climate threats.

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